1. Field of the Invention
The embodiments of present invention relate, in general, to a method of fabricating a thin film transistor and, more particularly, to a method of fabricating a thin film transistor adopting a solution process, in which metal patterns are formed through photo-reduction using a metal precursor dissolved in a solvent, thereby forming source and drain electrodes employed in the transistor. In more detail, the present invention pertains to a method of fabricating an organic thin film transistor, in which an electrode, an insulating layer, and a semiconductor layer are all formed through a solution process, thus it is possible to fabricate the organic thin film transistor having high charge mobility while the entire process is simplified and the fabrication cost is reduced.
2. Description of the Prior Art
Recently, studies have frequently been made of polymer materials as novel electric and electronic materials in wide fields, including functional electronic devices or optical devices, because the polymer materials can be easily shaped into fibers or films and are flexible and conductive, and because their fabrication costs are low. Of the devices using the conductive polymer, an organic thin film transistor employing organics as an active semiconductor layer has been studied since the year 1980, and many studies with respect to it are in progress over the whole world. The organic thin film transistor is advantageous in that, since it is possible to fabricate it through simple technology, such as printing technology, the fabrication costs are low and it has fair processibility and compatibility to flexible substrates.
Nowadays, it is predicted that the organic thin film transistor will be applied to driving devices of active displays, or plastic chips for smart cards and inventory tags.
The organic semiconductor thin film transistor employs polymer or oligomer as active material, which is a contrast to conventional amorphous silicon and polysilicon thin film transistors [F. Garnier et al., Science, Vol. 265, pp. 1684-1686; H. Koezuka et al., Applied Physics Letters, Vol. 62(15), pp 1794-1796; H. Fuchigami et al., Applied Physics Letters, Vol. 63(10), pp. 1372-1374; G. Horowitz et al., J. Applied Physics, Vol. 70(1), pp. 469-475; G. Horowitz et al., Synthetic Metals, Vol. 42043, pp. 1127-1130].
Conventional technology employing a solution process to fabricate an organic semiconductor thin film transistor has been suggested, but mainly applied to polymer and P-type organic semiconductors. The polymer semiconductors used to fabricate the organic thin film transistor are characterized by dissolution in an organic solvent, but low molecular weight organic semiconductors are characterized by being unsuitable for the solution process, thus it is nearly impossible to apply the solution process to low molecular weight organic semiconductors.
Furthermore, in a conventional method of fabricating the organic thin film transistor, electrodes are formed through a vacuum deposition process, but this method is problematic in that permeation and diffusion of metal occur in the course of forming source and drain electrodes, thus an insulator layer (for a bottom-contact structure) or an organic semiconductor layer (for a top-contact structure) is damaged.
Even though the organic thin film transistor has notable advantages in that, since it can be fabricated through a low-priced process, such as spin coating, spray coating, or ink-jet printing technology, the fabrication is simple and fabrication cost is low, it is used sparingly in applications in which high speed response and low voltage driving are required because charge mobility is low. Accordingly, there remains a need to develop an organic thin film transistor having high charge mobility.